1. Field of the Invention
The present invention relates to a pattern generation method and a charged particle beam writing apparatus, for example, a method of correcting a variable in pattern dimension caused by loading effects in pattern formation after electron beam writing to form a pattern on a target object and a writing apparatus and method for writing a pattern by using an electron beam on the target object.
2. Related Art
A lithography technique which leads development of micro patterning of semiconductor devices is a very important process which uniquely generates a pattern in semiconductor manufacturing processes. In recent years, with high integration of an LSI, a circuit line width required for semiconductor devices progressively decreases year after year. In order to form a desired circuit pattern on the semiconductor devices, a high-definition original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam writing technique has an essentially excellent resolution and is used in production of a high-definition original pattern.
FIG. 17 is a conceptual diagram for explaining an operation of a conventional electron beam writing apparatus.
A variable-shaped electron beam (EB) writing apparatus operates as follows. In a first aperture 410, a square, for example, rectangular opening 411 to shape an electron beam 330 is formed. In a second aperture 420, a variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 in a desired square shape is formed. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector. The electron beam 330 passes through a part of the variable-shaped opening 421 and is irradiated on a target object 340 placed on a stage. The stage continuously moves in one predetermined direction (for example, defined as an X direction). More specifically, a square shape which can pass through both the opening 411 and the variable-shaped opening 421 is written in a writing region of the target object 340. A scheme which causes an electron beam to pass through both the opening 411 and the variable-shaped opening 421 to form an arbitrary shape is called a variable shaped beam (VSB) scheme.
In the electron beam writing described above, a line width in a higher definition target object plane, for example, in a mask plane is required to be uniformed. In the electron beam writing, a phenomenon called a proximity effect disadvantageously occurs when an electron beam is irradiated on a mask to which a resist is applied to write a circuit pattern. This phenomenon is called a proximity effect caused by back scattering in which an electron passes through a resist layer, reaches a layer under the resist layer, and is incident on the resist layer again. For this reason, in writing, a variation in dimension occurs, i.e., a pattern is written in a dimension varying from a desired dimension.
On the other hand, furthermore, when a resist film is developed after writing or a film under the resist film is etched, a variation in dimension called loading effects caused by an area density of line segments of a circuit pattern disadvantageously occurs.
As a technique which corrects the proximity effect or the loading effects, the following description about the following contents is disclosed (for example, see Published Unexamined Japanese Patent Application No. 2005-195787 (JP-A-2005-195787)). In this case, an entire circuit pattern is divided in a 500-μm-square global loading effect small zone, a 0.5-μm-square proximity effect small zone, and a 50-nm-square micro-loading effect small zone. A map of influence quantity is formed. By using a dose (fixed value) at which a circuit pattern having a predetermined area density of 50% can be appropriately written, an exposure dose to write the circuit pattern is calculated. In this calculation, a proximity effect influenceability map and a map of proximity effect correction coefficients η calculated from a loading effect correction amount are used.
As described above, in charged particle beam writing typified by electron beam writing, a variation in dimension called loading effects occurs. As the loading effects, for example, a development loading effect of a resist film is given, or a Cr-loading effect occurring in etching of chromium (Cr) serving as a light-shielding film under the resist film is given. Furthermore, a loading effect or the like caused by a variation in pattern dimension in chemical mechanical polishing (CMP) is posed. On the other hand, in electron beam writing, a line width in a higher definition mask plane is required to be uniformed with a decrease in pattern line width. For this reason, loading effect correction which corrects a variation in dimension caused by the loading effects is performed. In this correction, a pattern is written in a state in which correction is performed at an amount of pattern dimension correction calculated to allow an amount of variation in dimension due to the loading effects in advance from a design line width of a circuit pattern (design pattern) A desired design line width can be obtained through loading effects caused by etching or the like. For example, when a calculated variation in dimension caused by the loading effects positively varies (to increase a line width), a circuit pattern is corrected in advance and then irradiated such that a line width is smaller than a design line width by the variation in dimension caused by the loading effects.
However, when a pattern is written with a line width smaller than a design line width, an area density (pattern density) of a circuit pattern obtained after the pattern writing is smaller than an area density (pattern density) of an original design pattern. For this reason, loading effects caused by etching or the like performed thereafter also decrease.
FIG. 18 is a diagram showing an example of a design pattern.
FIG. 19 is a diagram showing an example of a writing pattern obtained when the design pattern in FIG. 18 is written.
FIG. 20 is a conceptual diagram for explaining a line width of a pattern which is actually completed after etching when writing is performed with the dimension in FIG. 19.
When a pattern line width of an original design pattern 22 on a target object 20 such as a mask is given by CD0, a writing pattern 24 having a line width CDd(=CD0−2L) smaller than the pattern line width CD0 by an amount of variation in dimension L obtained by loading effects is written. However, as described above, the loading effects caused by etching or the like after the writing as described above become small. For this reason, an amount of variation in dimension L′ caused by actual positive loading effects also becomes small. As a result, a line width CDf of an actual circuit pattern 26 completed through an etching step is smaller than an expected design value (pattern line width CD0 of the design pattern 22). Consequently, a correction residual (L−L′) is disadvantageously generated.